Touch Your Plants? A Ticklish Question

By Eve Pranis

Try telling your students that in addition to watering and fertilizing their classroom plants, they might consider tickling them from time to time. You may get some quizzical glances.

The discovery that touch can affect how plants grow was accidentally made by two Stanford molecular biologists who had set out to study plant hormones. Discover Magazine reported that after spraying a particular hormone on a plant in the Mustard family, the researchers noted that five genes were activated. They found, much to their surprise, that the same genes were activated when the plants were sprayed with water, touched with fingers, or blown with a hair drier. They also observed concurrent changes in plant growth. When they kept up these treatments over three weeks, the touched plants were stocky and sturdy and grew to an average of 7 inches. Untouched "control" plants were more spindly and grew to an average of 16 inches.

Why might plants be tickled to toughness by touching? Consider the challenges of outdoor living. You and I can find shelter from strong winds and rain, but plants are rooted to one spot for a lifetime. Tall, spindly plants could snap in strong winds and harsh weather, while shorter, sturdier plants have a better chance of survival. The researchers theorize that this response to mechanical stimulation helps plants adapt to harsh outdoor conditions.

Do all plants respond in the same way? Do different types of stimulation (touch, water, wind, etc.) affect plants differently? How might the nature or frequency of touch affect plant growth? Do plants in exposed outdoor locations seem to grow differently than the same types in more protected areas? These are some questions yet to be explored.

Why not share these questions and invite your students to brainstorm some of their own, set set up experiments to test their ideas. Be sure to share with students that these researchers stumbled on this discovery accidentally. Remind them, when conducting experiments, to keep open minds and be prepared for the unexpected. Some of the world's most important scientific discoveries have been accidental. Remember penicillin?